While viruses usually produce particles in the infected cells, polydnaviruses (PDVs) have a very unusual virus life-cycle. Particle production does not occur in infected tissues of parasitized caterpillars, but is restricted to specialized cells of the wasp ovary. The genome enclosed in the particles encodes almost no viral structural protein, but mostly virulence factors used to manipulate the physiology of the parasitized host. This lack of virus genes in the packaged genome has generated a debate on the viral nature of PDVs. The characterization of a hidden bracovirus genome composed of virus genes, residing permanently in the wasp chromosomes and producing the particles, confirmed that bracoviruses originated from a virus. The viral machinery is comprised of genes typical of nudiviruses, a sister group of baculoviruses. The conservation of nudiviral genes in the various lineages of braconid wasps associated with bracoviruses strongly suggests that their common ancestor acquired a nudivirus genome 100 million years ago, which still controls the production of particles during viral replication